The present invention relates to an image scanner and more particularly to a high quality image scanner for scanning an image on a document.
Digital image processing, especially high quality color scanner image processing, provides high quality color images such as appear on a document. However, the long bit length for each color pixel requires an expensive analog-digital converter as well as an expensive CCD device, which necessarily increases the cost of the scanner. Also, the CCD has limited dynamic range.
Half-tone images have long been used in publication through printing. One of the more important areas in this activity is image editing, the rearrangement of the half-tone levels. Because there are so many limitations on printing, these limitations must be voided by image editing.
Printed materials are the means by which a designer expresses his ideas through publications. But digital printing processes can afford to express the half-tone images approximately less than 100-200 levels. This means that an image should be expressed in less than 100-200 levels. The images are printed as they were taken, but if the original image has large dynamic range, such as in color slides, there is a need to rearrange the tones of images to express the author's ideas more eloquently.
For example, even through the original image does not look bright, the author can impress a reader with bright images only if the image has larger dynamic range. It is said that half-tone images are required to have more than 8 bits/pixels, in general.
It is very important for the printing expert to arrange the grayness within the 100-200 levels. There are many techniques available to manipulate the grayness modification. In color printing processes, this is more important, because hue or color tones are more susceptible to the change of half-tone levels.